FIG. 25A shows a known secondary air supply system. This secondary air supply apparatus is designed to activate a three-way catalyst by introducing secondary air generated by operating an electric air pump 201 at the time of starting an internal combustion engine into a three-way catalyst converter (not shown) via a secondary airflow manifold and an engine exhaust manifold 202. In addition, a combination valve 203 formed of a lead valve having a non-return valve function and a diaphragm type flow opening valve is provided in the half way of the secondary flow manifold for introducing secondary air pressurized and supplied from the electric air pump 201 into the engine exhaust manifold 202 (for example, JP-7-158429A).
The secondary air supply apparatus is provided with a failure diagnosis function for diagnosing a failure of the electric air pump 201 and is designed to determine that the electric air pump is abnormal when the secondary air pressure detected by a pressure sensor 204 is out of a predetermined pressure range. The above combination valve 203 is provided with the lead valve and the flow opening valve formed integrally, which is different from the conventional secondary air supply apparatus. This arrangement causes downsizing of valve parts and reduction in manufacturing costs, and further makes possible prevention of corrosion or deposition of deposits in the secondary airflow manifold due to accumulation of an exhaust gas, flocculated water or the like therein. A diaphragm for opening and driving the flow opening valve, as shown in FIG. 25A, is operated by means of negative pressures via a vacuum switch valve 205.
A secondary air supply apparatus is proposed in consideration of both not only the conventional use in the level ground but also use in the upland region having low atmospheric pressures. This secondary air supply system is provided with a self-opening type flow opening valve (air switching valve) 206, as shown in FIG. 25B, for opening and driving a valve body by means of discharge pressures of the electric air pump 201 as a flow opening valve usable in both the uses (for example, JP-11-081998A). The electric air pump 201 is disposed in an upstream side of the flow opening valve 206 in the secondary airflow direction to be driven by receiving power from an in-vehicle battery for providing a desired secondary air pressure to the flow opening valve 206. The electric air pump 201 is designed to be controlled by an electrically controlled unit (ECU) via a relay for air pump control.
When a secondary air supply system is, however, used in the upland region under low atmospheric pressures, a secondary air supply system described in JP-7-158429A can not provide sufficient negative pressures necessary for operating a diaphragm which drives a valve body of the flow opening valve in the combination valve 203. In addition, in a secondary air supply system described in JP-11-081998A, the electric air pump 201 is located at a relatively distant position from the flow opening valve 206 the valve body of which opens by means of discharge pressures of the electric air pump 201 and therefore, the control responsiveness of the valve body of the flow opening valve 206 is not sufficient in view of a system function.
FIG. 26 shows a known evaporation fuel treatment system in which evaporation fuel evaporated in a fuel tank 211 for a vehicle such as an automobile is purged into an engine intake manifold 214 via a canister 212 and a purge vacuum switching valve 213 by means of intake manifold vacuum, thus preventing fluid such as the evaporation fuel from being discharged into an atmosphere. A throttle valve 215 is disposed in the intake manifold 214 and a normally-opening type canister control valve 216 is connected to the canister 212. Recently an intake manifold vacuum is likely to reduce in an internal combustion engine mounted in a hybrid car or a cylinder control type internal combustion engine. In this case, since the evaporation fuel is not sufficiently purged, there is provided a method of forcibly purging the evaporation fuel by an electric air pump. This method requires a flow opening valve for preventing leakage of fluid such as evaporation fuel at the time of ceasing the electric air pump, thereby deteriorating mount-properties to an engine room for a vehicle.
In view of the above, there exists a need for an electric air pump apparatus and an evaporation fuel treatment system which overcome the above mentioned problems in the conventional art. The present invention addresses this need in the conventional art as well as other needs, which will become apparent to those skilled in the art from this disclosure.